The present invention relates to a clutch for an automatic transmission and more particularly to a clutch drum for a clutch for an automatic transmission.
A known clutch drum of the above kind is shown in FIG. 1 which is disclosed in U.S. Pat. No. 4,267,910 issued to Yamamori et al. (see FIG. 1(A), a clutch drum 70). Referring to FIG. 1, an automatic transmission comprises a forward clutch 40 whose clutch drum 41 is splined to an input shaft 21 that is driven by a torque converter, not shown. The clutch drum 41 includes an outer tubular portion 41a engaged with a plurality of drive plates 42 for unitary rotation, an inner tubular portion 41d rotatably mounted to a stationary sleeve which is fixed to a transmission case, not shown, a disc portion 41e connected to both of the tubular portions 41a, 41d and defining a space between both of the tubular portions 41a, 41d for slidably receiving a piston 45, and a mounting portion 41f splined to the input shaft 21. Interleaved with the drive plates 42 are a plurality of driven plates 43 which are engaged in unitary rotation with an internal gear 53 of a planetary gear set. Extending through the input shaft 21 is an oil pump drive shaft 22 for driving an oil pump, not shown, which supplies fluid under pressure to fluid chamber 35 defined between the piston 45 and the disc portion 41e via fluid passage 41g and a circumferential groove 41k. Seals 41b are arranged to prevent fluid leakage via clearnace between the stationary sleeve 41c and the inner tubular portion 41d. When fluid pressure is supplied to the fluid chamber 35, the piston 45 is displaced to the right, viewing in FIG. 1, to press the driven plates 42 into engagement with the driven plates 43. This causes the internal gear 53 to rotate with the clutch drum 41. The clutch piston 45 is biased by a return spring 46 so that the clutch piston 46 assumes the illustrated position when the pressure in fluid within the fluid chamber 35 drops. Thrust washers, which serve as thrust bearings, are denoted by the reference numerals 41h, 41i and 41j.
The above mentioned clutch drum 41 features the mounting portion 41f which extends outwardly and axially from the inner tubular portion 41d. In other words, the mounting portion 41f is axially displaced from the inner tubular portion 41d. With this structure, a misalignment of the mounting portion 41f relative to the inner tubular portion 41d is amplified at the inner tubular portion 41d, resuting in a substantial amount of a radial displacement of the inner tubular portion 41d relative to the stationary sleeve 41c. Thus, when the fluid pressure in the fluid pressure chamber 35 is increased to displace the piston 45 relative to the clutch drum 41, a lefthand end, as viewed in FIG. 1, of the inner tubular portion 41d is pressed against the stationary sleeve 41c due to the reaction force applied to the clutch drum 41. This poses the following problems, i.e., the inner tubular portion 41d and the stationary sleeve 41c wear at their contacting surfaces, the seals 41b wear at a fast rate and thus are degraded quickly because the force with which the inner tubular portion 41d contacts with the seals 41b increases.